Advanced technologies like remote sensing have modified the way by which maps are constructed. Remote sensing is the procedure of collecting information about Earth with the help of instruments mounted on airplanes, satellites, or ships.
Remote sensing helps in monitoring and detecting the physical features of a region by determining its emitted and reflected radiation at a distance from the targeted region. Unique or specialized camera gather remotely sensed pictures of the Earth that assists the researchers in sensing the things about the Earth.
A 5-carbon base, C,A,G,T are the 5 bases available
I would guess C, hope that helps!